This invention relates to a wafer map display apparatus and method for a semiconductor test system, and more particularly, to a wafer map display apparatus which is capable of displaying an entire image of a semiconductor wafer and IC chips therein with an optimal display size within a specified window size even when there is no information available in advance on the number of IC chips or locations of the IC chips on the wafer.
A wafer map display apparatus is used in a semiconductor test system for displaying an image of each IC chip on a semiconductor wafer as well as overall characteristics of the wafer for easily and accurately observing the test results. The wafer map display apparatus provides important information for evaluating a semiconductor wafer from the standpoint of production yield and quality assurance in a semiconductor production process.
Because a display device (monitor) of a semiconductor test system is usually based on an operating system using xe2x80x9cwindowsxe2x80x9d, such a wafer map display is also displayed on the display device in a manner similar to other application tools using the windows. Therefore, a size of the window for displaying the wafer map is not adjusted in an optimum manner for the wafer display but frequently changed based on the operating system and application tools.
An example of conventional technology involved in such a wafer map display apparatus is explained below with reference to FIGS. 4 and 5. First, an entire structure of the semiconductor test system is shown in FIG. 4. In the example of FIG. 4, the system includes a test system main frame, a test station, a wafer prober, a workstation WS, a wafer map display apparatus, an external input means (key board and mouse, etc.), a storage medium (floppy disc, CDROM, hard disc, etc.), and a display device (monitor).
On a semiconductor wafer such as a silicon wafer, a plurality of IC chips to be tested are aligned in a matrix manner. The wafer prober is a handling device that can load, test, and unload semiconductor wafers one by one continuously in combination with the test station of the semiconductor test system. One or more IC chips are tested at the same time by connecting probe pins of the wafer prober to contact pads (electrodes) on the IC chips to establish electrical connection between the IC chips and the semiconductor test system for electrical communication therebetween for the purpose of testing the IC chips.
In the following description, it is assumed that each IC chip is tested one by one for illustration purpose. Thus, during the test, the test result for each IC chip and the X-Y address of the IC chip on the semiconductor wafer are obtained by the semiconductor test system one by one and sent to the workstation WS.
The semiconductor test system that is composed of the test system main frame and the test station electronically communicates with the wafer prober through the test station, and tests the IC chips on the semiconductor wafer in a predetermined order. Every time when one IC chip is tested, the semiconductor test system sends the test result (pass/fail) information and category information of the particular IC chip to the workstation WS, along with the chip address information of the IC chip on the semiconductor wafer through a communication network or line.
Upon receiving the test result information (which includes the chip address information on the wafer, pass/fail information in the test result, and the category information) from the semiconductor test system, the workstation WS provides the received information to the wafer map display apparatus. The received information is also stored in the storage medium.
The display device is a monitor which displays the test results and other information in a window format. It is rare for the display device used for the wafer map display of such a semiconductor test system that is set to a single window such as shown in FIG. 5A. Rather, as shown in FIG. 5B, the wafer map display screen is shown on the display device along with other windows of other application tools. Therefore, the window size for the wafer map display varies depending on the size of the other window applications. Moreover, the user can change the window size of the wafer map display through an input means such as a mouse.
In the conventional wafer map display application, the display size for each IC chip is fixed. Because of this, the window size required for displaying an entire semiconductor wafer varies when displaying a wafer of different number of IC chips or a wafer having different XY address alignment of IC chips. An example of a manner of displaying each IC chip is a color display such as using green and red based on the pass/fail information or a color display based on the category information.
An example of wafer map displays in the conventional technology is shown in FIGS. 5A and 5B. First, in the example of large window size (window A) in FIG. 5A, it displays all of the IC chips within the window A. However, since the display size of each IC chip is fixed, even though the window A of FIG. 5A is large enough, the wafer map of the overall semiconductor wafer W is displayed much smaller than the size of the window A. Thus, the display example of FIG. 5A has a large portion of unused space, as shown by an area C. In other words, the overall semiconductor wafer is not displayed in the optimal size.
FIG. 5B hows another display example in the conventional technology in which the display monitor shows windows D, F and G of smaller sizes. The window D shows images of IC chips CH and the semiconductor wafer W wherein not all of the IC chips CH (or entire semiconductor wafer W) are displayed within the window D. Therefore, in this example, the test results of the entire semiconductor wafer are not observed in one screen, and the user has to use a pointing device such as a mouse to scroll the display. Moreover, in this conventional example, it is not possible to easily observe the manner of distribution of characteristics of the IC chips over the entire wafer.
As mentioned above, the conventional wafer map display technology has a drawback in which it is not able to display the IC chips in an optimal size because the chip display size is fixed. Moreover, although the window size required for displaying the entire wafer varies when displaying a wafer of different size, or a wafer of different number of chips or a wafer with different chip alignment, the wafer map display cannot adjust the overall display size of the wafer because the chip display size is fixed. Furthermore, when the window size that displays the wafer map is small, it is burdensome and inconvenient for the user to evaluate the wafer and chips since the entire wafer and all of the chips cannot be displayed on the monitor at the same time.
Therefore, it is an object of the present intention to provide a wafer map display apparatus and method that is capable of displaying an entire wafer image with an optimal chip display size depending on the number of chips and the XY address information of the chips on the semiconductor wafer relative to the window size in the wafer map display without causing a substantial unused area in the window.
It is another object of the present invention to provide a wafer map display apparatus and method which is capable of calculating and changing an optimal chip display size to display an image of all of the IC chips that have been tested and an overall image of the semiconductor wafer within the specified window size every time when the test result of each IC chip is received from the semiconductor test system.
It is a further object of the present invention to provide a wafer map display apparatus and method of improved test efficiency and accuracy by displaying an image of the IC chips that have been tested with a maximum available size within the specified window size every time when the test result of each IC chip is produced by the semiconductor test system.
To achieve the above objectives, the first aspect of the present invention is a wafer map display apparatus for a semiconductor test system for testing semiconductor devices by displaying an image of IC chips on a semiconductor wafer based on test results. The wafer map display apparatus includes a window manager which is a display controller established based on an operating system of a personal computer or a workstation for displaying a wafer map of a semiconductor wafer under test in a specified window, means for acquiring window size information, means for acquiring IC chip information, means for storing the semiconductor wafer information, means for calculating a chip display size, and means for renewing the wafer map display.
An interface unit which is typically a format converter for window manager for converting the format of the data from the window manager to match with that of the units in the wafer map display apparatus. The interface unit periodically receives the window size information from the window manager and if the window size is changed, the window size information is sent to the calculating means for calculating a chip display size. The semiconductor test system communicates with the wafer map display apparatus and sends the IC chip information to the interface unit every time when an IC chip is tested.
Upon acquiring the IC chip information, an interface unit which is typically a format converter for test system for converting the format of the data from the semiconductor test system to match with that of the units in the wafer map display apparatus. The interface unit sends the information to the calculating means for calculating a chip display size and the chip information may be stored in the storing means in order to display the IC chip information on each image of IC chips on a wafer map. The calculating means determines a new size of IC chip display using both the window size and the XY address data. Then, the wafer map renewing means receives the new size of the chip display and the window manager refreshes the display screen to display a new wafer map based on the new size of the chip display.
Preferably, the chip display size is calculated every time when the window size information from the window manager is changed based on the XY address data of all of the IC chips that have been tested so that the images of the IC chips and the semiconductor wafer under test are displayed with a sufficiently large size or a maximum available size within the window size specified by the window manager. Alternatively, the chip display size is determined based on the window size information from the window manager and the chip display size obtained in the previous tests for the same kind of semiconductor wafer.
In the wafer map display apparatus, the semiconductor test system is able to test a plurality of semiconductor wafers in parallel at the same time and the window manager provides window size information to the window size acquiring means for displaying a plurality of windows on the wafer map display apparatus, whereby displaying a plurality of windows each showing a set of IC chips and the semiconductor wafer corresponding to the specified size of the window.
Another aspect of the present invention is a method of displaying a wafer map which is an image of IC chips on a semiconductor wafer based on test results to be implemented by a semiconductor test system for testing a semiconductor wafer. The method includes the steps of acquiring window size information from the window manager for displaying the wafer map of a semiconductor wafer under test in a specified window, calculating a chip display size every time when XY address data of an IC chip that has been tested is received from the semiconductor test system with use of all of XY address data of all of IC chips that have been tested up to the present, an renewing the wafer map display based on the newest chip display size determined by the calculating step, thereby displaying all of the IC chips that have been tested and an overall semiconductor wafer under test with an optimum size within the specified window.
Preferably, the step of calculating the chip display size includes a process of calculating the chip display size every time when the window size information from the window manager is changed based on the XY address data of all of the IC chips that have been tested so that the images of the IC chips and the semiconductor wafer under test are displayed with sufficiently large size within the window size specified by the window manager.
Alternatively, the step of calculating the chip display size includes a process of determining the chip display size based on the window size information from the window manager and the chip display size obtained in the previous test for the same kind of semiconductor wafer. When the chip display size is determined based on the previous test results of the other wafer, an IC chip is displayed with a size suitable for all of the IC chips on the semiconductor wafer can be displayed in one specified window even when the number of tested IC chips is substantially smaller than the overall number of IC chips on the semiconductor wafer under test.
A further aspect of the present invention is a zoom feature. In the present invention, if the number of the IC chips on wafer map is increased, the IC chip information on each IC chip cannot easily be read. In order to overcome the difficulty, the wafer map display apparatus of the present invention provides a zoom feature in which a predetermined or selected IC chip is enlarged on the display screen. For example, when a zoom command is received, the newest IC chip that has been tested is automatically selected and displayed in a zoom mode. If a zoom command with particular XY address data is received, the IC chip on the particular XY address may be displayed in the zoom mode.
According to the present invention, the wafer map display apparatus and method is capable of displaying the IC chips and semiconductor wafer with optimum size such as a maximum available size in the window even when the number of IC chips or XY chip address information is unknown in advance. The wafer map display apparatus and method of the present invention calculates the chip display size based on the test result information and displays the IC chips with colors and letters and the semiconductor wafer based on the calculated chip display size in an optimal size regardless of the number of IC chips within the window size. Therefore, the present invention substantially improves efficiency and accuracy of evaluating the IC chips and semiconductor wafers.